The Greenland-Norwegian Seaway: A key area for understanding Late Jurassic to Early Cretaceous paleoenvironments

joerg.mutterlose [ at ]


1] The paleoclimatology and paleoceanology of the Late Jurassic and Early Cretaceousare of special interest because this was a time when large amounts of marine organic matterwere deposited in sediments that have subsequently become petroleum source rocks.However, because of the lack of outcrops, most studies have concentrated on lowlatitudes, in particular the Tethys and the âBoreal Realm,â where information has beenbased largely on material from northwest Germany, the North Sea, and England. Theseareas were all south of 40°N latitude during the Late Jurassic and Early Cretaceous. Wehave studied sediment samples of Kimmeridgian (~154 Ma) to Barremian (~121 Ma) agefrom cores taken at sites offshore mid-Norway and in the Barents Sea that lay in a narrowseaway connecting the Tethys with the northern polar ocean. During the Late Jurassic-EarlyCretaceous these sites had paleolatitudes of 42â67°N. The Late Jurassic-Early Cretaceoussequences at these sites reflect the global sea-level rise during the Volgian-Hauterivian anda climatic shift from warm humid conditions in Volgian times to arid cold climates in theearly Hauterivian. The sediments indicate orbital control of climate, reflected in fluctuationsin the clastic influx and variations in carbonate and organic matter production. Traceelement concentrations in the Volgian-Berriasian sediments suggest that the central part ofthe Greenland-Norwegian Seaway might have had suboxic bottom water beneath an oxicwater column. Both marine and terrigenous organic matter are present in the seawaysediments. The Volgian-Berriasian strata have unusually high contents of organic carbonand are the source rocks for petroleum and gas fields in the region. The accumulation oforganic carbon is attributed to restricted conditions in the seaway during this time of lowsea level. It might be that the Greenland-Norwegian segment was the deepest part of thetranscontinental seaway, bounded at both ends by relatively shallow swells. The decline inorganic matter content of the sediments in the Valanginian-Hauterivian indicates greaterventilation and more active flow through the seaway as the sea level rose. The same benthicforaminifera assemblages are encountered throughout the seaway. Endemic assemblages ofarenaceous foraminifera in the Volgian-Berriasian give way to more diverse andcosmopolitan Valanginian-Hauterivian benthic communities that include calcareous species.The foraminiferal assemblages also suggest low oxygen content bottom waters during theearlier Cretaceous, changing to more fully oxygenated conditions later. The calcareousnannoplankton, particularly Crucibiscutum salebrosum, which is rare at low latitudes andabundant in high latitudes, reflect the meridional thermal gradient. They indicate that theGreenland-Norwegian segment of the seaway was north of a subtropical frontal zone thatacted as a barrier between the Tethyan and Boreal Realms. This implies the existence ofstable climatic belts during the early Valanginian and Hauterivian, significant meridionaltemperature gradients, and moderate ice-house conditions.

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DOI 10.1029/2001PA000625

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Mutterlose, J. , Brumsack, H. J. , Floegel, S. , Hay, W. W. , Klein, C. , Langrock, U. , Lipinski, M. , Ricken, W. , Soeding, E. , Stein, R. and Swientek, O. (2003): The Greenland-Norwegian Seaway: A key area for understanding Late Jurassic to Early Cretaceous paleoenvironments , Paleoceanography, 18 (1) . doi: 10.1029/2001PA000625

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